Prognostic significance of CT-determined sarcopenia in older patients with advanced squamous cell lung cancer treated with programmed death-1 inhibitors

Sarcopenia has been associated with higher toxicity induced by anti-cancer treatments and shorter survival in patients with squamous cell lung carcinoma (SqCLC). Over the past few decades, immune checkpoint inhibitors (ICIs) significantly improves the prognosis. However, few clinical studies explored the effectiveness of immunotherapy in the elderly population. Here, we performed a retrospective analysis to determine the prognostic role of sarcopenia in older patients with SqCLC receiving ICIs. We retrospectively assessed SqCLC patients who were treated with PD-1 inhibitors and all patients were at least 70 years old. Pre-treatment sarcopenic status was determined by analyzing L3 skeletal muscle index (SMI) with chest CT. Progression-free survival (PFS), disease-specific survival (DSS) and overall survival (OS) were estimated using the Kaplan–Meier method, and the differences in survival were compared using the log-rank test. Among 130 male SqCLC patients, 93 had sarcopenia. Patients with sarcopenia were older and had a lower body mass index (BMI). Over an average follow-up of 20.8 months, 92 patients died. For all 130 patients, the mean OS was 13.3 months. Patients with sarcopenia had a significantly shorter OS and PFS than those without sarcopenia (OS, 12.4 ± 5.2 months vs. 15.5 ± 10.5 months, P = 0.028; PFS, 6.4 ± 2.9 months vs. 7.7 ± 4.2 months; P = 0.035). Multivariable analysis showed that sarcopenia was an independent prognostic factor for shorter OS and PFS. CT-determined sarcopenia is an independent prognostic factor for older patients with SqCLC receiving ICIs.


Definition of sarcopenia
Dual-energy X-ray absorptiometry is the preferred go-to method for the measurement of skeletal muscle mass because of accuracy and repeatability 18 .However, this technology is not widely used in all departments of our hospital; therefore, pre-treatment (within one month) computed tomography (CT) was used to evaluate body composition to determine sarcopenia.CT scans were performed on a 320-row detector CT scanner (120 kVp tube voltage, automatic tube current), and reconstruction thickness was 1.25 mm.Two observers read and analyzed the CT images.We used the third lumbar vertebra (L3) skeletal muscle mass index (SMI) as an estimator of sarcopenia.The cross-sectional area of the skeletal muscle at the L3 level was measured using ImageJ software (National Institutes of Health, Bethesda, MD, USA).The skeletal muscle area included the psoas, erector spinae, quadratus lumborum, transversus abdominis, external and internal oblique, and rectus abdominis muscles.The CT HU thresholds were − 29 to + 150 for quantifying muscle 19 .The SMI was calculated as follows: SMI (cm 2 / m 2 ) = cross-sectional area (cm 2 )/height 2 (m 2 ).Sarcopenia was defined as an SMI < 52.4 cm 2 /m 2 for men, according to previous studies 15,20 .

Data collection
Baseline demographics, comorbidities (the age-adjusted Charlson comorbidity index score, A-CCI), eastern cooperative oncology group performance status (ECOG PS), previous treatment history, laboratory results, and PD-L1 positivity were collected.The ACCI was calculated by adding the comorbidity score and the age (Table 1) 21,22 .PD-L1 expression in the tumor samples was assessed by immunohistochemistry (IHC) using a PD-L1 IHC kit (22C3; Dako, Denmark) and characterized according to the tumor proportion score (TPS).
Response evaluation was performed using a CT scan of the target lesions and classified according to the immune-related response evaluation criteria in solid tumors 23 .Evaluations were performed every 8 weeks.The co-primary endpoints were PFS (the time from initial treatment to clinical or radiographic progression or death), DSS (the time from initial treatment to death due to cancer) and OS (the time from initial treatment to death due to any cause).Secondary endpoints included the objective response rate (ORR, the proportion of patients whose best overall response was complete or partial response [CR, PR]) and the disease control rate (DCR, the proportion of patients whose best overall response was CR, PR, or stable disease [SD]).
We also evaluated the safety.Patients were monitored for adverse events (AEs) from the first dose of study treatment to 90 days after the last dose.AEs were graded using the National Cancer Institute common terminology criteria for adverse events (version 5.0).

Statistics
Quantitative data were presented as mean ± standard deviation.The Kolmogorov-Smirnov test was performed to test for normality.Quantitative variables were compared using student's t-test for independent samples or the non-parametric Mann-Whitney test.Differences between categorical variables were compared using the chisquare test.Survival curves were constructed using the Kaplan-Meier method, and differences in survival were

Prevalence of and factors associated with sarcopenia
Among the 130 patients, 93 (71.5%) had sarcopenia based on the L3 SMI cutoff.Patients with sarcopenia had a mean SMI of 45.7 cm 2 /m 2 , whereas those without sarcopenia had a mean SMI of 57.1 cm 2 /m 2 (P < 0.001).As summarized in Table 2, patients with sarcopenia were older, had a lower body mass index (BMI), and were more frequently underweight than those without sarcopenia (12.9% vs. 5.4%).The proportion of ACCI scores ≥ 7 was significantly higher in the sarcopenia group than in the non-sarcopenic group (30.1% vs. 16.2%).However, no significant difference was found between two groups in terms of ACCI and smoking history.The majority of non-sarcopenic patients had an ECOG PS of 0-1 (75.7%), whereas 47.3% patients with sarcopenia had an ECOG PS of 2-3.Although the baseline levels of serum albumin, C-reactive protein (CRP), and interleukin 6 (IL-6) were comparable between patients with and without sarcopenia, the development of sarcopenia was significantly associated with lower albumin levels and higher CRP and IL-6 levels.
Previous treatment histories, such as surgery and radiotherapy, did not differ according to sarcopenic status; among the 130 patients, 103 received first-line chemotherapy, mainly paclitaxel or gemcitabine combined with platinum or paclitaxel alone.Seven patients received second-line treatment for general intolerance or other reasons, such as targeted drugs and docetaxel.There was no significant difference between the two groups in terms of the choice of chemotherapy regimen.

Discussion
In this study, we demonstrated that a high SMI was independently associated with a lower risk of mortality.To the best of our knowledge, this is the largest clinical study evaluating the association between skeletal muscle mass and outcomes in older patients with SqCLC who received ICIs.Currently, there are few studies on older patients with SqCLC.To fill this gap, our study included patients aged > 70 years with advanced SqCLC.All patients received ICIs, and the mean OS was 13 months, which is similar to the survival period of SqCLC reported in other studies.In our study, the OS, DSS and PFS of patients with sarcopenia were relatively shorter; therefore, SMI could be a useful variable for predicting prognosis.Cancer patients with sarcopenia often have a worse prognosis than cancer patients without sarcopenia.This may manifest as poor efficacy of chemotherapy or immunotherapy.Melanoma patients with sarcopenia are more likely to experience ipilimumab-related toxicity 24 , and patients with advanced NSCLC treated with nivolumab or pembrolizumab had poorer survival outcomes and response rates if they have sarcopenia 25 .Although the ways in which sarcopenia has a negative effect on the clinical efficacy of ICIs remain unclear, there are several potential explanations 26 .This could involve the interplay between the skeletal muscles and the immune system.Several animal experiments and epidemiological studies have revealed a causal relationship between chronic inflammation and tumorigenesis.Chronic inflammation also plays an important role in the development of sarcopenia, such as increased level of TGF-βand IL-6, which is a cause of muscle atrophy.These cytokines mediate T cell exhaustion, which causes immune dysregulation and resistance to ICIs 27 .Moreover, skeletal muscle, as an endocrine organ, secretes cytokines that regulate immunity and are involved in the modulation of the immune response 28 .This internal immune factor may explain the poor therapeutic effect and short survival period of patients with skeletal muscle reduction.
There are other important factors that need to be considered.Our study showed that patients with sarcopenia tended to be thin and had low plasma albumin levels.These patients have poor tolerance to chemotherapy and immunotherapy and are at a high risk of side effects, such as bone marrow suppression and other side effects after chemotherapy or immunotherapy.Although increased BMI has been shown to have protective effects on the prognosis of some patients with cancer 29,30 , some evidence suggests that obesity contributes to oncologic development and progression via chronic inflammation 31 .Therefore, BMI is not a perfect biomarker of body composition as it relies heavily on adiposity and cannot effectively represent body composition 32 .
We also discussed the impact of comorbidities on prognosis.In the study, we used ACCI to evaluate the incidence of comorbidities.It is worth noting that there is no difference in ACCI between the two groups and it cannot be used to predict prognosis.It's easy to understand that even if two patients have the same comorbidities, their physical functions can differ significantly.So ACCI cannot represent the overall situation.ECOG PS  www.nature.com/scientificreports/score is actually more suitable for evaluating the condition and treatment tolerance of the elderly.In our clinical work, we are also gradually carrying out comprehensive geriatric assessment (CGA) 33 .We believe that in future research, there can be a better evaluation system to comprehensively evaluate the function of elderly people.
Despite the novelty of this study, it had several limitations.First, this was a single-institution retrospective study with a small cohort.However, to the best of our knowledge, this is the largest study investigating the influence of skeletal muscle mass on clinical outcomes in older patients with SqCLC treated with PD-1 inhibitors.Second, this was a retrospective study and was subject to selection bias.We attempted to mitigate the effects of selection bias by including all patients treated at our center with available clinical data and baseline CT images.However, our patients were generally older and many had a history of smoking, which is often associated with cardiovascular and cerebrovascular diseases.We only analyzed whether ACCI can predict prognosis, but did not specifically discuss the impact of these underlying comorbidities on patient survival.Third, due to the application of multiple anti PD-1 drugs in our study, there may be differences in treatment efficacy caused by differences in the agents.Finally, we only included skeletal muscle as a surrogate for body composition and did not include other marker such as contents of fat.In future research, we can explore the impact of changes in body composition on the prognosis of patients receiving immunotherapy, not limited to muscle mass.
In conclusion, baseline sarcopenia was associated with significantly poorer outcomes after PD-1 inhibitor treatment in older patients with advanced SqCLC.In clinical practice, screening for sarcopenia can help identify patients who are likely to achieve a long-term response.
Table 5. Incidence of all-cause AEs and immune-mediated AEs.AE adverse event.a Treatment-related adverse events occurring in 15% or more of patients in either group were listed.Events are shown in descending order of frequency in the sarcopenia group.b Immune-related adverse events occurring in 3% or more of patients in either group were listed.

Table 2 .
Baseline patients characteristics.SD standard deviation, BMI body mass index, ACCI the ageadjusted Charlson comorbidity index, CRP C-reactive protein, IQR interquartile range, IL-6 interleukin 6, SMI skeletal muscle mass index, PD-L1 programmed cell death protein 1 ligand 1, EGFR epidermal growth factor receptor, TKI tyrosine kinase inhibitor.a Eastern Cooperative Oncology Group performance status (ECOG PS) ranges from 0 to 5, with 0 indicating no symptoms and higher scores indicating greater disability.

Table 3 .
Response to treatment according to sarcopenic status.Data are represented as number of patients with percentages.

Table 4 .
Multivariate analysis of factors influencing OS and PFS.PFS progression-free survival, OS overall survival, HR hazard ratio, CI confidence interval, BMI body mass index, ACCI the age-adjusted Charlson comorbidity index, PD-L1 programmed cell death protein 1 ligand 1, TPS tumor proportion score.a Eastern cooperative oncology group performance status (ECOG PS) ranges from 0 to 5, with 0 indicating no symptoms and higher scores indicating greater disability.